Apparatus and method for generating cut surfaces in the cornea of an eye for correction of ametropia

ABSTRACT

A method for generating cut surfaces in the cornea of an eye in order to correct ametropia using an apparatus. The method includes providing the apparatus including a laser unit, which focuses pulsed laser radiation into the cornea and moves the focused radiation in the cornea to generate cut surfaces, and a control unit, which controls the laser unit for generating cut surfaces. The method includes forming at least two mutually spaced apart cut surfaces as opening cuts by application of the pulsed laser radiation from the laser unit, each opening cut extending from an anterior corneal surface into the cornea and forming a further cut surface as a relieving cut by application of the pulsed laser radiation from the laser unit, which relieving cut extends from the anterior corneal surface into the cornea. The position and shape of the relieving cut is selected such that the relieving cut contributes to the correction of the ametropia of the eye.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/109,917filed Apr. 25, 2008 and entitled Apparatus and Method for Generating Cutsurfaces in the Cornea of an Eye for Correction of Ametropia whichclaims priority to German Application No. 10 2007 019 813.4, filed Apr.26, 2007 and to U.S. Provisional Application No. 60/914,177 filed Apr.26, 2007, the disclosures of all of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an apparatus for generating cut surfaces in thecornea of an eye in order to correct ametropia, said apparatuscomprising a laser unit, which can focus pulsed laser radiation forgenerating cut surfaces into the cornea and move the radiation therein,and a control unit, which controls the laser unit for generating cutsurfaces such that a predetermined lenticle to be removed is separatedfrom the surrounding corneal material in the cornea by at least one cutsurface and such that at least two mutually spaced apart cut surfacesare formed as opening cuts, each extending from the lenticle to theanterior corneal surface.

The invention further relates to a method for generating cut surfaces inthe cornea of an eye in order to correct ametropia, wherein the pulsedlaser radiation for generating cut surfaces is focused into the corneaand moved therein such that a predetermined lenticle to be removed isseparated from the surrounding corneal material in the cornea by atleast one cut surface and such that at least two mutually spaced apartcut surfaces are formed as opening cuts, each extending from thelenticle to the anterior corneal surface.

2. Background

Such apparatus and method are known, for example, from WO 2004/105661A1. However, the desired correction of ametropia of the eye isfrequently not achieved by such apparatus and method.

SUMMARY OF THE INVENTION

In view thereof, it is an object of the invention to improve anapparatus of the above-mentioned type to overcome the describeddisadvantage. Further, a corresponding method of the invention isimproved accordingly.

Said object is achieved by an apparatus of the type mentioned above forgenerating cut surfaces in the cornea of an eye in order to correctametropia in that the position and shape of the opening cuts areselected such that the opening cuts contribute to the correction of theametropia of the eye or do not counteract the correction of theametropia of the eye.

It has been discovered that the opening cuts themselves, although beingvery small, may lead to an undesirable deterioration of the eye'sametropia. Since this effect of the opening cuts is now being taken intoaccount for the first time by the apparatus of the invention, thisadvantageously allows the opening cuts to contribute to the correctionof ametropia or not to counteract the correction of the eye's ametropia.The opening cuts according to the invention accomplish the foregoingadvantages because they are neutral with respect to the ametropia to becorrected and/or do not cause any additional ametropia. Thus, forexample, when correcting myopia or hyperopia, the opening cuts can beprevented from causing an undesired astigmatism.

Thus, the apparatus according to the invention for generating cutsurfaces in the cornea of an eye in order to correct ametropiaadvantageously benefits from the fact that an opening cut, which is tobe provided and through which the lenticle can be removed, is alsosimultaneously taken into account with respect to the correction of theeye's ametropia. It has turned out that favorable results can beachieved by providing two or more opening cuts. Providing two or moreopening cuts has the advantage that they can be used, for example, torinse the area being operated on (cut area of the lenticle).

Further, the inclusion of the opening cuts in the correction ofametropia is advantageous insofar as the lenticle volume to be removedcan be minimized. Thus, reductions in thickness from several μm up to100 μm can be achieved. This allows, for example, minimizing mechanicalweakening of the cornea, if such weakening is caused by material removalor lenticle removal, respectively.

The opening cuts are provided such that it is not possible to fold backa corneal lamella as in the known LASIK operation (laser in situkeratomileusis). Thus, the opening cuts do not lead to a flap of thetype provided and folded back in the LASIK operation.

The ametropia to be corrected may be, for example, myopia, hyperopia,astigmatism or presbyopia. It is also possible for the present inventionto correct higher-order errors of refracting power. In particular,fourth-order errors of refracting power (spherical aberrations) lead toproblems with night vision. Thus, these errors of refracting power ofthe cornea, or ametropias, can also be corrected by the apparatusaccording to the invention.

The present control unit may control the laser unit to thereby generateat least three mutually spaced apart opening cuts such that the centersof area of the opening cuts coincide with the corners of a regularpolygon. In this case, it is possible, for example, that the openingcuts do not cause additional astigmatism.

The geometrical shape may be the same for each opening cut, although itis also possible to select different geometrical shapes. Thus, forexample, the control unit may control the laser unit such that the cutlength of at least one opening cut from the anterior corneal surface tothe lenticle differs from the cut length of the other opening cuts.

Further, the control unit may control the laser unit to generate exactlytwo mutually spaced apart opening cuts such that the centers of area ofthe opening cuts are located on a straight line which, when viewed in atop view of the eye, is parallel to one axis of astigmatism of the eyeor intersects said axis at a maximum angle of 10°. This enables acorrection for astigmatism. Preferably, the steepest axis of astigmatismis selected (i. e., that axis in relation to which the greatestastigmatism is present).

The control unit can control the laser unit such that at least one ofthe opening cuts, when viewed in a top view of the eye, has thegeometrical shape of a circular ring segment. This shape can be realizedwith particular ease using conventional laser units in ophthalmiccorrection apparatuses.

In particular, the control unit can control the laser unit such that theopposite straight sides of the circular ring segment enclose an angle of30°-120°, 45°-80°, or 30°-60°.

Further, the control unit can control the laser unit such that theopposite straight sides of the circular ring segment have a length of0.1-1 mm or 0.2-0.4 mm, when viewed in a top view.

In the apparatus according to the invention, the control unit cancontrol the laser unit such that a further cut surface is provided as arelieving cut, which extends from the anterior corneal surface into thecornea, but not up to the lenticle. The location and shape of therelieving cut may be selected so as to contribute to the correction ofthe eye's ametropia. Of course, several relieving cuts can be provided.Due to the additional relieving cut or cuts, an effective correction ofametropia can be achieved.

The control unit can control the laser unit such that at least one ofthe cut surfaces is generated as a perforated cut surface. A perforatedcut surface is understood herein to be a cut surface which is notentirely continuous, but comprises material bridges which break awayunder a predetermined mechanical load (for example, by removal of thelenticle).

In a method of the above-mentioned type, the location and shape of theopening cuts are selected such that they contribute to the correction ofthe eye's ametropia or do not counteract the correction of the eye'sametropia.

Using the method according to the invention, it is therefore possible toprovide the required opening cuts such that they contribute to thecorrection of ametropia or do not counteract the correction ofametropia. This makes it possible to minimize the material volume of thelenticle to be removed. In particular, the lenticle need not beprovided, for example, to compensate for imaging errors caused by theopening cuts, which would otherwise disadvantageously lead to a greatermaterial volume to be removed from the cornea.

In the method of this invention, the position and shape of the openingcuts may be selected such that the correction of the ametropia of theeye is not counteracted in such a manner that the opening cuts do notgenerate additional astigmatism of the eye. This makes it possible tocorrect myopia or hyperopia in which the patient, while no longer beingnear-sighted or far-sighted, has an ametropia in the form of anastigmatism.

The ametropia to be corrected may be myopia, hyperopia, astigmatismand/or presbyopia. The ametropia may further comprise higher-ordererrors of refracting power, as well. In particular, the ametropia mayinclude fourth-order errors of refracting power such as sphericalaberration, which plays a major role in night vision capacity.

In the method of this invention, at least three mutually spaced apartopening cuts can be generated such that their centers of area coincidewith the corners of a regular polygon. In this case, it is probable thatthe opening cuts will not cause additional astigmatism.

The cut length of at least one opening cut from the anterior cornealsurface to the lenticle may be made to differ from the cut lengths ofthe other opening cuts. The opening cuts may also have the same ordiffering geometrical shapes and/or dimensions.

In one method of the invention, exactly two mutually spaced apartopening cuts can be generated such that their centers of area arelocated on a straight line which, when viewed in a top view of the eye,is parallel to an axis of astigmatism of the eye (preferably thesteepest axis of astigmatism) or intersects said axis at a maximum angleof 10°. Such spaced apart opening cuts enable effective correction ofastigmatism.

These opening cuts may be executed such that at least one of the openingcuts, when viewed in a top view of the eye, has the geometrical shape ofan circular ring segment. Such a shape can be easily realized using alaser unit of a conventional ophthalmic correction apparatus.

In particular, the opening cut may be carried out such that the oppositestraight sides of the circular ring segment enclose an angle of30°-120°, 45°-80°, or 30°-60°.

Further, the at least one opening cut may be carried out such thatopposite straight sides of the circular ring segment have a length of0.1-1 mm or 0.2-0.4 mm.

In one present method, a further cut surface may be formed as arelieving cut, extending from the anterior corneal surface into thecornea, but not up to the lenticle. The position and shape of therelieving cut may be selected such that the cut contributes to thecorrection of the ametropia. One or several mutually spaced apartrelieving cuts can be formed, the opening cut(s) enable(s) improvingcorrection of ametropia.

In one present method, at least one of the cut surfaces may be formed asa perforated cut surface, thereby resulting in smoother cut surfaces, ascompared to cut surfaces produced as continuous cut surfaces by pulsedlaser radiation.

In particular, one method of this invention allows the lenticleseparated from the surrounding corneal material to be removed from thecornea through one of the opening cuts.

It is further possible to divide the lenticle into two or more parts bythe pulsed laser radiation and to remove said parts of the lenticle fromthe cornea through one or more opening cuts.

Further, the opening cuts may also be used to effect flushing of the cutsurfaces or, where applicable, to introduce drugs.

Further, a method is provided for generating control data for a controlunit of a correcting apparatus for generating cut surfaces in the corneaof an eye. The correcting apparatus may comprise a laser unit and acontrol unit. The laser unit may focus pulsed laser radiation into thecornea in order to generate cut surfaces and move said radiationtherein. The control unit for the laser unit generates control data,thereby allowing the control unit to control the laser unit, on thebasis of the control data to generate cut surfaces, such that apredetermined lenticle to be removed is separated from the surroundingcorneal material in the cornea through at least one cut surface and suchthat at least two mutually spaced apart cut surfaces are provided asopening cuts. Each opening cut may extend from the lenticle to theanterior corneal surface. The position and shape of the opening cuts maybe predetermined by the control data, such that the opening cutscontribute to correction of the ametropia of the eye or do notcounteract the correction of the ametropia of the eye.

The present method for generating control data may be further embodiedsuch that further embodiments of the inventive method for generating cutsurfaces in the cornea of an eye in order to correct ametropia can becarried out.

The cut surfaces may be generated in the cornea using the apparatusaccording to the present invention and the present method by pulsedlaser radiation. Several processes may take place in the tissue within atime sequence. These processes may be initiated by pulsed laserradiation. If the power density of the radiation is above a thresholdvalue during any pulse, an optical breakthrough may appear, which, forexample, would form a plasma bubble in the cornea. The plasma bubblethen grows, due to expanding gas after the optical breakthrough hasformed. If the optical breakthrough is not maintained, the gas generatedin the plasma bubble is absorbed by the surrounding tissue, and thebubble disappears. Tissue-separating effects, acting without plasmabubbles, are also possible. For the sake of simplicity, all suchprocesses, including their effects, are summarized here by the term“optical breakthrough.”

For tissue separation to occur, the laser radiation may be applied inpulsed form, with the pulse duration usually being below 1 ps. Thus, thepower density required for the respective pulse to initiate the opticalbreakthrough is achieved within a narrow spatial area. High focusing ofthe laser beam in combination with the short pulses allows the opticalbreakthrough to be placed in the cornea with pinpoint accuracy. For cutsurface generation, a series of optical breakthroughs is generated atthe corresponding locations for the cut surface.

It will be appreciated that the features mentioned above and those yetto be explained below can be used not only in the indicatedcombinations, but also in other combinations or alone, without departingfrom the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below, by way of exampleand with reference to the enclosed drawings, which also disclosefeatures essential to the invention and wherein:

FIG. 1 shows a schematic view of an embodiment of the correcting deviceaccording to the invention;

FIG. 2 shows a top view of an eye after carrying out the methodaccording to the invention for generating cut surfaces in the cornea ofan eye for correction of ametropia;

FIG. 3 shows a cross-sectional view of the cornea H along the line 17 ofFIG. 2;

FIG. 4 shows a top view of an eye after carrying out the correctingmethod of the invention according to another embodiment;

FIG. 5 shows a top view of an eye after carrying out the correctingmethod of the invention according to yet another embodiment;

FIG. 6 shows a top view of an eye after carrying out the correctingmethod of the invention according to another embodiment;

FIG. 7 shows a top view of an eye after carrying out the correctingmethod of the invention according to yet another embodiment; and

FIG. 8 shows a top view of an eye after carrying out the correctingmethod of the invention according to another embodiment.

DETAILED DESCRIPTION

In the embodiment shown in FIG. 1, the apparatus 1 for generating cutsurfaces in the cornea H of an eye A in order to correct ametropiacomprises a laser unit 2 and a control unit 3 for control of the laserunit 2. Further, the apparatus 1, which is also referred to hereinafteras a correcting apparatus, may comprise a contact element 4 which isdetachably coupled with the laser unit 2 and with which the eye A to becorrected is in contact during operation of the apparatus 1.

As is evident from the schematic representation of FIG. 1, the laserunit 2 comprises a laser 5 emitting pulsed laser radiation 6. In thiscase, the pulse duration is, for example, in the femtosecond range (e.g.50-800 fs) at a pulse repetition frequency of between 10 and 1 MHz.

The pulsed laser radiation 6 is focused through the contact element 4,by two deflecting mirrors 7, 8 forming a scanner 9 and by optics 10,into the cornea H of an eye A contacting the contact element 4 and ismoved in the cornea H. This is effected under the control of the controlunit 3, so that basically any locations in the cornea can have thepulsed laser radiation 6 applied thereon.

Of course, the scanner may also be designed in any other manner known tothe person skilled in the art.

The control unit 3 may control the laser unit 2 such that an opticalbreakthrough for tissue separation is generated at the respective focuslocation in the cornea H. The focus locations are selected to beadjacent each other such that a desired cut surface can be generated inthe cornea H. The focus locations may be adjacent each other such thatthe tissue is cut through completely between the focus locations.However, it is also possible that small tissue bridges remain, so thatthe cut surface can be referred to as a perforated cut surface.

The laser unit 2 and the control unit 3 are shown in a schematic andsimplified manner in FIG. 1. Thus, for example, the optics 10, depictedas a lens, may comprise several optical elements, suitably arrangedalong the beam path from the laser 5 to the contact element 4.

The correction apparatus 1 may be operated such that, in order tocorrect ametropia (in this case, for example, correction of myopia andastigmatism), a preferably lens-shaped partial volume 11 (hereinafteralso referred to as a lenticle) in the cornea H is separated from thesurrounding corneal material by the pulsed laser radiation 6. This ispreferably carried out such that first the rear surface 12 (FIG. 3) ofthe lenticle 11 and then the front surface 13 of the lenticle 11 is cut.In order to allow the lenticle 11, separated from the residual cornealmaterial, to be removed from the cornea H, first and second opening cuts14, 15, each extending from the lenticle 11 to the anterior cornealsurface 16, are provided, as schematically shown in FIGS. 2 and 3.

The lenticle 11 can then be removed from the cornea H in a known mannerthrough the first or second opening cut 14, 15. Due to the missingcorneal volume (lenticle 11), the cornea will change its shape in thisarea. Prior to carrying out the method, the shape of the lenticle wasselected such that the shape of the cornea after removal of the lenticleresults in the desired correction of ametropia.

In the described exemplary embodiment of FIGS. 2 and 3, two opening cuts14 and 15 have been performed and the shapes and positions of theopening cuts 14 and 15 are selected such that any still existingastigmatism of the eye A is also corrected thereby.

In other words, the invention takes into consideration the fact thateven the very small opening cuts 14 and 15 may have an influence on theastigmatism of the eye A. This per se undesired effect is used in theinvention to correct an existing astigmatism of the eye A.

In the described exemplary embodiment, it is assumed that the steepestaxis of astigmatism in FIG. 2 extends from top to bottom as indicated bythe arrow P1. In this case, the two opening cuts 14 and 15 are arrangedsuch that their centers of area S1 and S2 are located on a straight line17, which is parallel to or coincides with, the axis of astigmatism P1.Merely for the sake of clearer illustration, FIG. 2 shows the axis ofastigmatism P1 slightly laterally of the straight line 17.

By this arrangement of the opening cuts 14 and 15, the astigmatism ofthe eye A is reduced due to the opening cuts 14 and 15.

As is evident from FIG. 2, the opening cuts 14 and 15, when viewed inthe top view of FIG. 2, are respectively provided as circular ringsegments. Since both opening cuts 14 and 15 are identical, only thefirst opening cut 14 will be described in more detail below.

The two straight sides 18 and 19 of the opening cut 14 have the samelength T (FIG. 2), said length being between 0.1 and 1 mm or between 0.2and 0.4 mm in the exemplary embodiment described here. Further, the twostraight sides 18 and 19 enclose an angle α, which may range from30°-120° or from 40°-80°.

FIG. 4 shows a modification of the embodiment of FIGS. 2 and 3. In thismodification, the opening cuts 14 and 15 are placed such that thestraight line 17 connecting the centers of area S1, S2 encloses an angleγ with the axis of astigmatism P1, said angle being 10° here. Even withthis modification, an excellent correction of astigmatism is stillachieved by the opening cuts 14 and 15.

As is evident from the embodiment shown in FIG. 5, three opening cuts14, 15 and 20 have been carried out. The opening cuts 14, 15 and 20 aremutually spaced apart, with the centers of area S1, S2 and S3 defining atriangle, which is indicated by a dotted line in FIG. 5.

In order to achieve a correction of astigmatism by the opening cuts 14,15 and 20, the opening cuts 14, 15 and 20 are located at unequal angulardistances from one another on the circumference of the lenticle 11, asis evident from FIG. 5. Thus, the angle β₁ is 150° and the angles β₂ andβ₃ are each 105°. Due to this asymmetrical angular distribution of theopening cuts 14, 15 and 20, the desired correction of astigmatism isachieved.

However, it is also possible to distribute the opening cuts 14, 15 and20 at equal angles, as shown in FIG. 6. In this case, the angles β₁, β₂and β₃ are each 120°. This distribution of the opening cuts is selectedif no correction of astigmatism by the opening cuts 14, 15 and 20 isdesired. This may be the case, for example, if no astigmatism, but onlya myopia has to be corrected. Thus, the opening cuts 14, 15 and 20 canbe provided such that there is no influence on the astigmatism. As isevident from FIG. 6, the triangle defined by the centers of area S1, S2and S3 is then an equilateral triangle.

Further, it is possible for the opening cuts 14, 15 and 20 in FIG. 6 tobe arranged and shaped such that they contribute to the desiredcorrection of myopia.

Providing the opening cuts without influencing the astigmatism of thecornea H is also possible in the case of four opening cuts, as shown inFIG. 7. The four opening cuts 14, 15, 20 and 21 are again distributed atequal angles on the circumference of the lenticle 11 so that, in thiscase, the centers of area S1, S2, S3 and S4 define a square.

In general, it can be said that n opening cuts (with n>2) can beprovided such that their centers of area form a regular n-sided polygonso as to cause no influence on astigmatism by the n opening cuts.

As indicated in FIG. 8, which shows a further development of theembodiments of FIGS. 2 and 3, relieving cuts 22, 23 can be carried outin addition to the opening cuts 14, 15, said relieving cuts extendingfrom the anterior surface of the cornea H into the latter, but not up tothe lenticle 11. These relieving cuts 22, 23 can be used in order tocorrect the ametropia to be corrected by the lenticle 11 and/or of theastigmatism (arrow P1).

The invention claimed is:
 1. A method for generating cut surfaces in acornea of an eye in order to correct ametropia using an apparatus, saidmethod comprising: providing the apparatus including a laser unit, whichfocuses pulsed laser radiation into the cornea and moves said focusedpulsed radiation therein in order to generate cut surfaces within thecornea, and a control unit, which controls the laser unit for generatingcut surfaces; forming at least one cut surface as an opening cut byapplication of the pulsed laser radiation from the laser unit, theopening cut extending from an anterior corneal surface into the cornea;forming a further cut surface having several relieving cuts byapplication of the focused pulsed laser radiation from the laser, theseveral relieving cuts extending from the anterior corneal surface intothe cornea; and selecting a position and a shape of the severalrelieving cuts such that the several relieving cuts contribute to thecorrection of the ametropia of the eye.
 2. The method as claimed inclaim 1, further comprising selecting a position and a shape of eachopening cut such that the opening cuts do not counteract the correctionof the ametropia of the eye.
 3. The method as claimed in claim 1,further comprising generating at least one of the cut surfaces as aperforated cut surface.
 4. The method as claimed in claim 1, furthercomprising selecting a position and a shape of each opening cut suchthat the opening cuts do not generate any additional astigmatism of theeye.
 5. The method as claimed in claim 1, wherein the ametropia to becorrected comprises an astigmatism of the eye.
 6. The method as claimedin claim 1, further comprising using the at least one of the openingcuts to rinse an area being operated.
 7. The method as claimed in claim1, wherein the pulsed laser radiation is generated with a pulse durationbelow 1 ps.
 8. The method as claimed in claim 1, forming at least twomutually spaced apart cut surfaces as opening cuts by application of thepulsed laser radiation from the laser unit, each opening cut extendingfrom the anterior corneal surface into the cornea.
 9. A method forgenerating cut surfaces in the cornea of an eye in order to correctametropia using an apparatus, said method comprising: providing theapparatus including a laser unit, which focuses pulsed laser radiationinto the cornea and moves said focused radiation therein in order togenerate cut surfaces within the cornea, and a control unit; controllingthe laser unit with the control unit to form at least two mutuallyspaced apart cut surfaces as opening cuts by application of the pulsedlaser radiation from the laser unit, each opening cut extending from ananterior corneal surface into the cornea; and selecting a position and ashape of each opening cut such that the opening cuts contribute to thecorrection of the ametropia of the eye.
 10. The method as claimed inclaim 9, further comprising: forming a further cut surface as arelieving cut, which relieving cut extends from the anterior cornealsurface into the cornea; and selecting a position and a shape of therelieving cut such that the relieving cut contributes to the correctionof the ametropia of the eye.
 11. The method as claimed in claim 10,wherein several relieving cuts are formed and a position and a shape ofeach relieving cut is selected such the relieving cuts contribute to thecorrection of the ametropia of the eye.
 12. The method as claimed inclaim 9, further comprising generating at least one of the cut surfacesas a perforated cut surface.
 13. The method as claimed in claim 9,further comprising selecting a position and a shape of each opening cutsuch that the opening cuts do not generate any additional astigmatism ofthe eye.
 14. The method as claimed in claim 9, wherein the ametropia tobe corrected comprises an astigmatism of the eye.
 15. The method asclaimed in claim 9, further comprising using the at least one of theopening cuts to rinse an area being operated.
 16. The method as claimedin claim 9, further comprising generating the pulsed laser radiation isgenerated with a pulse duration below 1 ps.